Valve controlled hydraulic actuating device



April 29, 1958 A. P. HENRY 2,832,317

VALVE CONTROLLED HYDRAULIC ACTUATING DEVICE Filed May 1.7, 1955INVENTOR.

HTTOENE Y ALGUSTL/ P HENRY United States Patent i ice VALVE CONTROLLEDHYDRAULIC ACTUATNG DEVICE Augustus P. Henry, Los Angeles, Calif.,assigner, by mesne assignments, to Kelsey-Hayes Company, Detroit, Mich.,a corporation of Delaware Application March 17, 1955, Serial No. 494,957

6 Claims. (Cl. 121-41) This invention relates to new and usefulimprovements in a valve controlled hydraulic actuating device.

A valve controlled hydraulic actuating device, as that phrase is usedherein, is a device incorporating both an input element and an outputelement, which output element is sensitive to positional changes of theinput element relative to a fixed reference frame and is instantlyresponsive to said positional changes. In such a device, also, the powerlevel, or stroking force, of the output element is very much greaterthan the power level, or stroking force, at the input element,hereinafter called the valve.

The power medium is a source of pressurized fluid supplied by anexternal agent. The iluid is generally but not necessarily a relativelyincompressible tluid such as a mineral base oil, and the external agent(pump) is presumed to be capable of supplying pressurized fluid insuiiicient volume and at a regulated pressure so that the Huid supply`to the device exists at essentially constant high pressure (say 3000 p.s. i.) regardless of the Volumetric demands of the valve controlledactuating device.

A cardinal aim of the present invention is to provide a new and improvedservo mechanism. A servo mechanism is a device which is capable ofaccepting an input signal of a low power level and which is capable ofcontinuously adjusting the position of its output element at a highpower level so as to maintain the system instantaneous errorcontinuously at a` small magnitude and ideally zero in a steady statecondition. Said steady state condition is that which exists after alltransients have died out or otherwise relaxed. The instantaneous error,in the sense this phrase is used herein, is the absolute positionaldifference, at any instant of time, which exists between the position ofthe input element (valve) and the corresponding position of the outputelement. Thus, as in any servo mechanism, the motivating influence whichgoverns the positional condition and the changes in the positionalcondition of the output element of the present invention is theexistence of and the condition of an instantaneous error; such errorbeing the lack of correspondence between the position of the inputelement (valve) and the position of the output element, both positionsbeing relative to the same reference frame. In speaking of the positionof the valve, there is meant the position of a movable member, as alongitudinally displaceable valve spool, in the valve.`

The present invention embodies within its combination means forcontinuously comparing the position of the input element, as, forexample, the valve spool longitudinal displacement, relative to theposition of the output element; which latter is hereinafter referred toas the actuator.v In addition means are provided within theVcornbinaticm of the present invention whereby the actuator will adjustits position according to any lack of correspondence between thepositions of the input ele 27,832,317. Patented Apr, 29,` 1958 ment(valve) and of the output element (actuator) so that said lack ofcorrespondence will cease to exist. Thus the actuator will follow up, ina positional sense, the positional Variations of the valve spool whichis under continuous positional control by an outside agent.

The present invention concerns itself with a valve controlledhydraulically powered servo actuating device which is of particularusefulness as a component in the primary llight control system of apiloted aircraft, including such usefulness in the automatic navigationand re control subsystems.

The present invention does not concern itself with the type of feedbackloop employed for comparison of the position of the input elementrelative to the position of the output element. The several meanswhereby this comparison may be made are Well known in the state of theart.

The present invention provides within its structure by virtue of theunique cooperation of its several coacting elements means whereby thedevice is capable of accepting one or the other of two controllinginputs with resulting controlled output positioning of, say, anaircraftiiight control surface, with in such case the controlling inputeither that supplied by the human pilot: or that supplied by anautomatic pilot.

The primary object of this invention is to provide a multi-functionvalve controlled hydraulic actuating device which combines the severalcontrol functions within the single structure, which combination offunctions is characterized by reliability, and which structureisplicable, so that said design shall be compatible in all respects withthe requirements imposed upon said design by the peculiar dynamiccharacteristics of the airframe in which it is to be used.

In exemplication of the invention, a now preferred ernbodiment thereofis shown in the accompanying drawing; the figure of which is across-sectional View of the device, taken in a vertical plane includingthe longitudinal center line of the actuator. It will be noted that thisView is partially schematic, to clarify and simplify the disclosure.

Referring now in detail tothe structure thus illustrated,

reference numeral 1 designates the shaft extensions of the valve spool.Secured to one shaft extension of the valve spool is clevis 2, to whichlatter the mechanical link from the pilots control stick or column isattached.

The valve spool is shown as comprised of a constant diameter shank 3 onwhich are three enlarged diameter lands. The central land is designatedi, and the two outboard lands are designated 5 and 6; said shank, landsand end shaft extensions being integral with one another. The threelands are in intimate sliding relationship with the sleeve 7, thereby toprovide sealing means for isolating fluid in the annular chamber d `fromfluid in the annular chamber 9 and from uid in the annular chambers 10and ii. formed beyond the outboard lands 5 and 6 and between them, theshaft extensions i 'md the valve sealing bushings i?, and Sleeve 7 ispositioned in a longitudinal bore in housing le. End caps id and 16 aresuitably'secured to, herein shown as threaded into, housing 14, toprevent endwise shifting et sleeve? 7 and of the sealing bushings 1;.and 1,3.

Housing 14 is shown as an integral unit not only to house the inputelement (the valve as just above partially described), but also iixedlyto carry the output element. As will be noted the housing 14 is hatchedmerely over portions of the section thereof shown; this in order furtherto clarify the drawing while keeping it as simple as possible.

The valve sleeve 7 and the bushings 12 and 13 are provided with O-ringstatic seal members 17 at their outside diameters. These seal members 17prevent leakage bctween any of the points of varying pressure levelalong the outside of the sleeve 7 in the longitudinal bore through thehousing 14 between the end bushings 12 and 13. The end bushings 12 and13 are also provided with O- ring sliding seal members 18 which preventleakage of fluid from chambers and 11 around the valve spool shaftextensions 1.

Fluid at a constant high pressure Ps, assumed admitted through asuitable threaded fitting (not shown) applied as at 19, enters anannular groove 20 machined into the outer surface of sleeve 7. Fluid isdischarged at nominally atmospheric pressure PX through a suitablethreaded fitting (not shown) applied at 21. Communicating with outlet 21is external annular groove 22 of the valve sleeve 7; and said groove 22,by way of several interconnected drilled passages in housing 14, thesepassages collectively diagrammatically indicated at 23, is connectedwith external annular groove 24 of the valve sleeve 7. Fluid at highpressure PS in annular groove 2t) is guided toward valve spool land 4through one hole or a suitable series of holes one of which is indicatedat 25, and also toward said valve spool land 4 through one hole or asuitable series of holes one of which is indicated at 25.

Fluid at return line pressure PX in annular groove 22 is guided towardvalve spool land 6 through one hole or a suitable series of holes one ofwhich is indicated at 26; and uid at said pressure Px in annular groove24 is guided toward valve spool land 5 through one hole or a suitableseries of holes one of which is indicated at 27.

Said holes or sets of holes 25, 25, 26 and 27 are drilled or otherwiseformed in the fixed valve sleeve 7; and desirably with said holes insets, each hole set 25, 25', 26 and 27 is formed of a multiplicity ofholes whose center lines, while preferably extended to intersect thevalve center line at right angles thereto, are spaced longitudinally ofthe sleeve 7 so that as the valve spool is displaced one hole afteranother opens in planned sequence. This longitudinal spacing of theholes of a set makes it possible to obtain a valve characteristic whichis linear, that is, a valve flow rate proportional to valve spooldisplacement.

As the valve spool is displaced, say to the right of the figure, chamber8 of the valve is opened to high pressure Huid in annular chamber 20, byway of said hole or set of holes 25 and through a restricted orifice orequivalent of a restricted orifice formed by land 4 and said hole orhole set 25. Simultaneously fluid in valve chamber 9 is constrained toow through the restricted orifice or equivalent formed by land 6 andsaid hole or hole set 26; the design of the parts being such as to giveto the last-mentioned orifice or equivalent, at any extent of spooldisplacement to the right, the same cross-sectional area as afforded atthe same instant by the orifice or orifice equivalent constituted by thehole or holes 2S.

The orifice or orifice equivalent constituted by the hole or hole set 26connects as already stated with annular groove 22, which latter leads tothe outlet at 2l.

When, on the other hand, by appropriate movement of the pilots controlstick or column, its connection to the clevis 2 causes valve spooldisplacement to the left of the figure, chamber 9 of the valve is openedto high pressure fluid in annular chamber 20, by way of said hole orhole set 25 and through a restricted orifice or orifice equivalentformed by land 4 and said hole `or .2,832,317 I j f hole set 25'.'Simultaneously uid in valve chamber 8 is constrained to flow through therestricted orifice or equivalent formed by land 5 and said hole or holeset 27 the design of the parts being such as to give the lastmentionedorifice or equivalent, at any extent of spool displacement to the left,the same cross-sectional area as afforded at the same instant by theorifice or equivalent constituted by the hole or holes 25.

And, also, as already stated, the orifice or orifice equivalentconstituted by the hole or hole set 27 connects with the outlet 21-byway first of the annular groove 22 and next by way of the passagescollectively diagrammatically indicated at 23 as aforesaid, and next 'byway of annular groove 20.

.Further formed on the valve sleeve 7 are external annular grooves 28and 29, the former being open as at 23 to the valve chamber 8 and thelatter being open as at 29 to the valve chamber 9.

A conduit delineation is diagrammatically given at 3Q, this representinga plurality of appropriately intersecting drilled passages in housing14, leading from said annular groove 28 in the valve sleeve to the endportion 31 of the piston chamber of the actuator adjacent to theactuator end bushing 32. The end bushing 32, provided with O-ring sealmembers as shown, is, interruptedly around around its inner periphery atits inner face, relieved by a series of radially dispersed slots asindicated at 30 for maintaining open communication between the drilledpassages just above referred to and the end portion 31 of the pistonchamber of the actuator.

Another conduit delineation is diagrammatically given at 33, this alsorepresenting a plurality of appropriately intersecting drilled passagesin housing 14, but with these leading from the annular groove 29 in thevalve sleeve to the end portion 34 of the piston chamber of the actuatoradjacent to the actuator end bushing 35. The end bushing 35, providedwith lO-ring seal members as shown, is, interrup-tedly around its innerperiphery at its inner face, relieved by a series of radially dispersedslots as indicated at 33 for maintaining open communication between thedrilled passages last above referred to and the end portion 34 of thepiston chamberof the actuator.

The actuator piston rod has an extension 36 which is secured rigidly, asat 37, to airframe structure 38. An enlarged diameter section on thepiston rod forms piston head 39, which latter is provided with an 0-ringseal member as indicated. Piston head 39, a sleeve 40, the portion ofthe piston rod to the left of the piston head, and actuator end bushing35, form actuator chamber 34, that is, the end portion of the pistonchamber of the actuator adjacent to said end bushing 35. Similarly,piston head 39, sleeve 4i), the portion of the piston rod to the rightof the piston head, and actuator end bushing 32, form actuator housingchamber 31, that is, the end portion of the piston chamber of theactuator adjacent to said end bushing 32. Said sleeve 40 is shown asprovided with O-ring seal members as indicated.

Operation under control of hmmm pilot This, as aforesaid, is effected bythrust or pull from the control stick or column, applied longitudinallyof the valve spool, as at the clevis 2.

On displacement of the valve spool to the right, consequent upon such athrust, valve action takes place as previously described, that is, fluidis caused to flow, via 20 land 25, into valve chamber 8, and thence, via28, 23 and 30, to the actuator chamber 31. Simultaneously, also aspreviously described, fluid is permitted, via 26 and 22, to ow out ofthe valve chamber 9, and hence, via 33, 29 and 29', from the actuatorchamber 34.

Therefore, the volume of actuator chamber 31 is made to increase, whilethe volume of actuator chamber .34 is permitted to decrease, bothchanges in volume being precisely equivalent.

asseoir Because the actuator piston rod extension 36 is secured tostructure, said volumetric changes constrain the actuator housing 14,with the result that actuator extension 41 is forced to move to theright. This motion will continue until the movement of the valve sleeve7 (fixed within and transported with housing i4) is Sullicient to blockoil orifice or orifice equivalents 2 and 25.

Carried -by the actuator is attach point 42 whereby connection is had toan aircraft control surface actuating horn.

On displacement of the valve spool to the lelt, as the result of a pullfrom the pilots control stick or column, the valve action, also aspreviously described, is such that fluid is caused to flow, via and 25',into the valve chamber 9, and at the same time, via 27 and 24, to flowout of the valve chamber 8, and hence, via 36, 28 and 28', from theactuator chamber 3l.

In this case, the volume of actuator chamber 34 is made to increase,while the volume of actuator chamber 31 is permitted to decrease, bothchanges in volume being precisely equivalent.

Again, because the actuator piston rod extension 3o is secured tostructure, said volumetric changes constrain the actuator housing 14,now with the result that actuator extension 4i is forced to move to theleft; and this motion will continue until the movement of the valvesleeve 7 is suilicient to block ot oriiice or orifice equivalents and2'7.

Thus always during control of the aircraft by the human pilot and by wayof the hydraulic servo as illustratively shownl and described herein,the valve spool position, relative to a reference plane iixed in theaircraft, is enslaved to the position of the pilots stick or column. Thehydraulic servo `as herein shown and described has inherent unityfeedback, although this one to one feedback ratio is not necessarily arequirement of the invention.

The follow up action of the actuator 4i causes it to respond to changesof position of the valve spool relative to the sleeve 7 in which itoperates. As the outside agent-the human pilots manual input, causes aninitial displacement ot' the valve spool relative to structure, thisinitial displacement is relative to the actuator, as that is initiallystationary. The valve sleeve l7, at the same time, is lixed relative tothe actuator housing 14, which latter, it will be recalled, is themovable output element.

As will also 'be recalled, any displacement 0f the valve spool relativeto the sleeve 7 in which it operates,

results, by the coaction of the several lands 4, 5 and 6 included in thevalve spool conriguration and spaced apertures in the sleeve 7, in theformation of sets of restricted area openings through which pressurizedfluid is constrained to llow to and from otherwise isolated chambers (31and 34) within the actuating element. This iiow causes a correspondingchange in the position of the actuator 41-and also of housing 114, onwhich il is alixed; such change in position being at a rate proportionalto the volumetric llow rate through the several metering ports formed bya valve spool displacement relative to the sleeve 7 in which itoperates.

This condition exists until the actuator has moved to its newequilibrium position, at which position the actuator will have displaceditself and with it the valve l sleeve 7 to that precise position wherethe valve ports tion of a by-pass valve, permitting a short circuitrelative to said chambers While the system is under manual control. Suchby-pass valve, which as is well-known in the hydraulics art ischaracterized by the inclusion of a valve member movable to one positionwhereat flow through the valve is permitted and to another positionwhereat liow through the valve is cut off, is indicated `at 44. At 45 isrepresented a conduit for connecting said end chamber 10 with the valve44, and at 46 is represented a conduit for connecting said end chamberll with the valve 44, in such manner that in the rstmentioned, or open,position, of the valve member in Valve 44, the conduits 4S and 46 areinterconnected, While in the second-mentioned, or closed, position ofthe valve member in the valve 44, the conduits 45 and 46 are out off onefrom the other. During operation under control of the human pilot, thevalve 44,` being then `with its Valve member in said open position,functions to prevent hydraulic lock because of liuid at any time and inany amounts in the valve end chambers 10 and 11.

rThe said by-pass valve 44 should be as close, hydraulically speaking,to the main valve spool `and chambers i@ and ll; as possible in order tominimize damping forces at the valve spool. Excessive spool dampingfeels like mass (inertia) reflected to the vpilots control station.

In the illustrative showing of a by-pass valve, at 44, the sameincludes, it will be noted, a valve spool 34 urged toward valve openingposition by a spring 87 but held to vaive closing position by a solenoid33 when energized by electrical input through a connection from theautopilot.

The means for at the proper times throwing the valve to open or closedcondition, and for simultaneously throwing a hereinbelow described valveSe to closed or open condition, according as supply of the control inputis to be from the human pilot or the autopilot, may be of any kind, forinstance manual, as solenoid and pushbutton means, or solenoid meansenergized in agreement with a manual throwing in or out of theautopilot.

As herein shown the system incorporates an actuator piston 39, which isa 'balanced area one, and consequently the control valve, or inputelement, is of the type cornmonly termed in the hydraulic art a four-wayvalve; but as will be understood, the design could be such that aso-called three-way valve could be employed as the control valve orinput element with then the actuator piston an unbalanced area one.

Azltopz'lot control Next to consider provisions of the presentinvention, as present in the illustrative embodiment thereof hereinshown and described, whereby to permit control input to be 'wheneverdesired that supplied by the automatic pilot* it will be noted that theactuator piston rod which carries the balanced area actuator piston 39is in the form of a tubular shaft 4'7 containing a bore in which isslidingly contained a smaller balanced area piston 48 integral with apiston rod 49. The piston 4S, herein called the autopilot responsepiston, is movable relative to the piston 39, in which connection it ispointed out that the piston rod 49 is secured as at Sii to the actuatoroutput member 4l.

Actuator piston rod extension 36 is shown as threaded into the lett handend of the actuator piston rod and also as provided with a static G-ringseal member to .make liuid tight the coupling of said extension 36 tothe actuator piston rod. Said extension is tubular as indicated, forentry therein of the left hand extension of the piston rod 49, and isprovided with a sliding O-ring seal member as indicated, to preventleakage between the left hand end extension of piston rod 49 andactuator piston rod extension 3d. Said tubular shaft 47 constituting theactuator piston rod is provided at its righthand estension with abushing 5ft. Bushing 54 is provided with a static O-ring seal member asindicated to prevent fluid leakage between said bushing 'and tubularsha-ft 47 and also with a sliding -ring seal member as indicated toprevent iluid leakage between said bushing and the right hand extensionof piston rod 49. ln addition piston rod 43, as aforesaid integral withpiston rod (i9, is provided with an O-ring seal member as indicated toprevent lluid leakage from one side of said piston to the other.

At 56 is indicated an electro-hydraulic transfer valve of the typewell-known in the hydraulics art. The two chambers 57 and 5% establishedin the bore of the hollow piston rod d'7, at the opposite sides of theautopilot response piston 4S, are served by the transfer valve 56 Whilethe autopilot is functioning. At that time, also, the by-pass valve 44has its valving member closed7 iso lating conduit d5 from conduit 46.

ln the illustrative showing of an electro-hydraulic transfer valve, at56, the same, it will be noted, is a fourway valve and includes a valvespool 82 at the opposite ends of which are solenoids 8G and Sli forpositioning the valve spool in accordance with electrical signalstransmitted through a connection S6 from the autopilot.

Conduit not only, as already stated, communicates with the left handvalve spool chamber lll, land with by-pass valve dei (which now, thatis, for autopilot operation, is closed), but also with autopilottransfer valve 56, and with piston chamber S7 at the left hand side ofthe autopilot response piston 48. Said conduit 45 is shown as openinginto the said left hand valve spool chamber 1t) by way of a drilledpassage S9 in valve sleeve 7, and as connected with said piston chamber57 by way of the drilled passages 60 in piston rod 49 and an* nulargroove 61 of the actuator extension 4l.

Conduit 46 not only, vas already stated, communicates with the righthand valve spool chamber ll, and with said by-pass valve 44, but alsowith autopilot transfer valve S6, and with piston chamber 53 at theright hand side of the autopilot response piston d3. Said conduit de isshown as opening into the right hand valve spool chamber l1 by way of adrilled passage 63 in valve sleeve 7, and as connected with said pistonchamber 58 by way of the drilled passages 64 in piston rod i9 andannular groove 65 of the actuator extension ill.

As further regards either conduit i5 or d6, said conduit is partiallyformed of appropriately intersecting drilled passages in housing 14 andpartially formed of external plumbing or tubing external of housing id.

Operation under autopz'to control Assume that the device initially is atrest stationary. A signal, electrical in nature, is accepted by theelectro-hydraulic transfer valve 56. Recall in this connection that thedevice is a servo mechanism. Therefore the signal which is accepted byvalve S6 represents an instantaneous error or lack of correspondencebetween the actuator present output position and the actuator outputposition commanded by the autopilot. This mean ing of instantaneouserror, as the phrase is used herein, has been explained hereinabove.

Say that the autopilot commands the actuator to move to the right. Thetransfer valve 56 ports pressurized tiuid into conduit 4S whilesimultaneously allowing iluid to ilovv out of conduit 46. Conduit i5 asalready stated communicates with chamber 5'1". initially, chamber 57cannot accommodate the change in volume through conduit 45 because theprimary actuator is hydraulically locked by the pressurized uid trappedin actuator chambers 3l and 345. Because conduit 45 communicates withthe valve spool chamber 1t), as above described, the initial volumetricchange supplied by the transfer valve 56 must necessarily beaccommodated by a corresponding increase in the volume contained invalve chamber 10. This is possible because the valve spool is slidablerelative to sleeve '7 in which said spool operates.

Initially, then, from a position of rest, flow from transfer valve 56into conduit de' results in displacement to the right of the main valvespool relative to sleeve 7 in which it operates. Immediately, theactuator output member di, in the manner as has been described herein(in discussing operation under control of human pilot), moves to theright at a rate proportional to the displacement of the valve spoolrelative to said sleeve 7 in which it operates. Actuator output motionresults in an increase in volume of chamber S7, which volumetric rate ofincrease is precisely proportional to the actuator linear velocity. Atthis time the increasing volume of chamber 57 is able to accommodate thevolumetric delivery of the electrohydraulic transfer valve 56 withoutfurther displacement of the valve spool relative to said sleeve 7 inwhich it operates.

lt is to be noted that the volumetric delivery of transfer valve 56 isaccommodated by the sum of the volumetric change of valve spool chamber10 plus the volu- L metric change of chamber 57.

(For a steady state velocity to the right, say, the transfer valve isreceiving a constant amplitude signal from its associated error sensorand amplifier, and is delivering iiuid ata constant rate into theconduit 4S. This constant volumetric rate is being accommodated by theconstantly increasing 'volume of chamber 57, which volumetric in creaseis caused by actuator output at a constant linear velocity to the right,which velocity is a result of main valve spool fixed displacement to theright relative to sleeve 7.

(Thus for a commanded constant actuator output velocity, a unique mainvalve spool position relative to its coasting sleeve is called for. Ifthe main valve spool is displaced at any point other than said uniquepoint, the internal loop, that is, the self compensating feature justabove described, between the autopilot response piston and the mainvalve spool in the sleeve 7, immediately results in said valve spooldisplacing itself relative te said ti i) v quired and described aboveare satisfied.)

Simultaneous with the admission of fluid through transfer valve S6 intoconduit 45, decreases in volume of valve spool chamber ll plus decreasein volume in chamber 5S of the outopilot response piston is dischargedfrom conduit 46 through the transfer valve 5,6, the ow into conduit 45being precisely equivalent to the flow out through conduit ed.

The above described action continues until the initial auto-pilotcommand is satisfied. This condition of correspondence between theactuator output position and autopilot command is detected by theautopilot feedback sensor. Said sensor may be, but is not necessarily apotentiometer as indicated schematically in the ligure. Thepotentiometer is shown as consisting of a resistive element 66 fixed tostructure 3S and having a voltage impressed across its terminals 67 and63. A wiper point 69 is in physical contact with resistive element 66and moves relative thereto, as the main valve, to whose end extension'70 it is fixed, moves while being transported by housing 14. Thus thevoltage between wiper 69 and terminal 67 or 68 is a measure of actuatoroutput position (less the displacement of tbe main valve spool relativeto the sleeve 7 and hence relative to the actuator housing lli). Thisvoltage is transmitted to the autopilot ampliiier wherein in a mannerwell understood in the art it is subtracted from autopilot commandinput, the ditierencc resulting being by delinition the autopilot error.

As the actuator output position changes in response to an autopilotcommand, the autopilot error diminishes. Reduction of autopilot errorsimultaneously reduces the ow rate through the autopilot transfer valve56, and allows the actuator output velocity to diminish with (andresulting from) a reduction in the displacement of the asseoir @i mainvalve spool relative to its co-actiug sleeve '7. Si multaneously, as theautopilot error is reduced to zero, the flow through the autopilottransfer valve reduces to zero, the main valve spool attains its neutralposition relative to the sleeve 7 in which it operates, and actuatoroutput motion stops.

For an autopilot command calling for actuator motion to the left, asymmetrically opposite set of events takes place. Fluid admitted by thetransfer valve d into conduit 46 with a correspondingly equivalent flowout of conduit db'. initially an accommodating incr-cae in the volume ofvalve spool chamber il, displaces he valve loop to the left relative tothe sleeve in which it operates. Main valve action results in actuator'motion to the left. The then resulting increase in volume of cham ber 53accommodates the flow into conduit 46 and thus prevents or otherwiselimits further relative displacement of the main valve spool. Suchaction continues until the autopilot command is satislied, at whichpoint the autopilot transfer valve 56 discontinuos its porting of fluidinto conduit lo while simultaneously the main valve spool re-centersitself and actuator output motion stops.

ln the structure shown in the figure, the chamber formed within actuatorrod extension 3d is shown as suitably vented to atmosphere by means ofdrilled hole 7l. Likewise the chamber 72 located at the right handextension of tubular piston rod is vented to atmosphere by means ofdrilled hole Such venting is necessary in order to eliminate anypossibility of trapped fluid in chamber 53 and/or in chamber 72inhibiting the controlled positional changes of the output member.

Schematically indicated in the ligure are a conduit "75 for supplyingthe pressurized liuid and leading to the main valve inlet 19, a conduit'7o branching from the conduit 75 and leading to the autopilot transferval e 56; and also a conduit 77 for receiving from the main valve outlet2l iluid at nominally atmospheric pressure, and a conduit 7S leading tesaid conduit 77 and for receiving from the autopilot transfer valve 56iluid at nominally atmospheric pressure.

As will now be understood, the present invention at tains theintegration within a single package of the functions of a dual inputservornechanism. The inputs may (as described hereinabove, but notnecessarily) originate at a control station which is manned by a humanope"- ator, as, for instance, a human pilot, or at a control stationwhich accepts automatic signals, as, for instance, an electro-hydraulictransfer valve responsive to electrical signals from an autopilot.

By means of integration of functions as described, the single actuator,in conjunction with the main valve spool ends, performs functions of twoactuating clements. ln a practical sense this means that one separateactuator has been eliminated ln the illustrated case the autopilotactuator as a separate item has been dispensed with. The advantagesattained allow for weight and volume reduction, ease of maintenance, andbecause of system simplification a general enhancing of system ovcrallreliability is achieved.

It can be shown mathematically that the composite system as described intl e foregoing specification is dynamically precisely equivalent to aconventional system with autopilot tie-in under the followingrestrictions (a) lf the area of the main valve end tcnfrnber lil orchamber il, the two being equal in area) is equal to the area of thereplaced autopilot actuan (o) And if, at the saine time, the area of theautopilot response piston (chamber or chamber 5E, the two being equal inarea) is equal to ar a. of the main valve spool ends (chamber l@ orchamber lll).

lf the area of the autopilot response piston is less than (b), thecomposite system stability margin decreases. An extreme case is when theautopilot response piston area is Zero, that is, the response piston isomitted entirely.

Under such conditions the system tends to become oscillatory and underactual real load conditions would likely become unstable, which is tosay that the amplitude ofoscillation increases with time.

On the other hand if the area olf the response piston is made largerthan (la), system stability margin can be increased. rthis is a verygreat advantage as it provides the designer with an additional newdesign parameter for' adjusting subsystem stability to be compatiblewith complete system (including airframe) dynamic requirements. This upto now has always been a serious problem. Because of the relativelysmall areas involved, increasing response piston area is not normally adifficult design task.

lt is to be appreciated that the system with autopilot tie-in accordingto the present invention is of great usefulness in both fixed and rotarywing aircraft. control systems. The system can be of widespreadusefulness, moreover, in other than aircraft applications such as, forexample, in ship and submarine steering, machine tool control and thelike.

As will be understood, only one of the various possible embodiments ofthe invention has been shown. This has been described with considerableparticularity of detail, not for purpose of limitation, of course, butto illustrate the various capabilities of the invention. As will beunderstood, variations and modifications are possible, and parts of theimprovements may be used without others. The scope of protectioncontemplated is to be taken primarily from the appended claimsinterpreted as broadly as is consistentwith the prior art.

i claim:

l. A hydraulically actuated servo mechanism comprising, in combination,a control valve, an input element constituted by a valve spool includedin said valve, an output element movable in either of two directions,means whereby said output element is moved in one of said two directionsor the other according as said valve spool in response to an input fromone source is moved in one direction or the other, and an auxiliarymeans responsive to receipt thereby from a source other than thefirstnamed one of an input in either of two directions for coacting withsaid valve to cause said output element to move in one or the other ofsaid two directions according as the input from the said other source isin one or the other of said two directions, said valve spoolintermediate its ends carrying a plurality of lands and the controlvalve having two end chambers each outward of said lands, tl efirst-named means including cylinder and piston means and conduit meansconnecting the latter and the interior of the control valve elsewherethan at said outward chambers, and the said auxiliary means includingother cylinder and piston means, said auxiliary means including said twoend chambers of the control valve and an electro-hydraulic transfervalve and conduit means connecting said transfer valve with said endchambers and also with the cylinder of said auxiliary means at theopposite sides of the piston thereof, there being a oy-pass valveoperatively associated with said end chambers effective when opened toprevent hydraulic lock at said end chambers while said transfer valve isinoperative.

2. A hydraulically actuated servo mechanism 'comprising in combination,a control valve, an input element constituted by a valve spool includedin said valve, an output element movable in either of two directions,means whereby said output element is moved in one of said two directionsor the other according as said valve spool in response to an input fromone source is moved in one direction or the other, and means responsiveto receipt thereby from a source other than the first-named one ol aninput in either of two directions for coaction with said valve to causesaid output element to move in one or the other of said two directionsaccording as the input from the said other source is in one or the otherof said two directions, said valve spool intermediate its ends aesasivcarrying a plurality of lands and the control valve having 'two chamberseach outboard of said lands, the secondnamed means including saidoutboard chambers, the first-named means including cylinder and pistonmeans and conduit means connecting the latter and the int of the controlvalve elsewhere than at said outbo chambers, the second-named meansincluding other cylinder and piston means, there being a hydraulicsystem including both the iirst-named and the second-r. means, and meansin said system variable at will operationally excluding from said systemor inch in said system the second-named means, said variabre meansincluding a valve means so interposed in sai system that in one settingof said valve means said secondnamed means is operative and in anothersetting of l5 valve means said second-named means is inoperative, saidvalve means including electro-hydraulic tr sier valve and a by-passvalve, said variable means further including a conduit means having aconduit between. said transfer valve and one of said outboard chambersand a branch from said conduit connecting it with said oy-pass valve andalso another branch from sail:` conduit connecting it with thesecond-named cylinder and piston means at an end portion ot its cylinderat one side of its pistou, and said variable means further including aconf3.5 duit means having a conduit between said transfer vulve and theother of said outboard chambers and a brat h from the last-named conduitconnecting it with said ol,- pass valve and also another branch fromlast-r ned conduit connecting it with said secondmamed cylinder S0 andpiston means at an end portion of its cylinder at the other side of thepiston.

3. A hydraulically actuated servo mechanism comprising, in combination,a control valve, input ele constituted by a valve spool in said valve,an output element movable in either of two directions, a housing lixedlycarying said output element, means inclu ine conduit means forpressurized tiuid whereby sia-id or element by action of said fluid canbe moved in one ci direction or the other, and an auxiiiary means resooito receipt thereby from a source other than the li named one of an inputin either of two directions f coaction with said valve to cause theoutput elenent more in one or the other of said two directions accordingas the input from said other source is in one or the c" of said twodirections, the sleeve of said valve be ixedly carried by said housing,the first-named including a cylinder and piston couple e cylinder ofwhich is constituted by a chambering An said housing, said coupleincluding a tubular piston rod carryi there being a second cylinder andpiston coi the cylinder is inside said tubular piston rod and of wb thepiston is secured to the housing, said valve spool inter mediate itsends having a plurality ot' lands thereon e the control valve havi g twochambers each outboard u said lands, said auxiliary means includin" bersand an electro-hydraulic transfer connecting transfer valve with saidbers and also with the cylinder or said second con opposite sides of thepiston of said conin by-pass valve operatively associated vc. said adcham- `bers effective when opened to prevent hydra iic lock at auxiliarymeans responsive to receipt thereby from a source other than thefirst-named one of an input in either of two directions for coactionwith said valve to cause the output element to move in one or the otherof said two directions according as the input from said other source isin one or the other of said two directions, the firstnamed meansincludinga cylinder and piston couple the cylinder of which isconstituted by a chambering in said housing, said couple includingy atubular piston rod carrying the piston, there being a second cylinderand piston couple of which the cylinder is inside said tubular pistonrod and of which the piston is secured to the housing, said spoolintermediate its ends having a plurality of lands thereon and thecontrol valve having two chambers each rutboard of said lands, saidauxiliary means including said end chambers and an electro-hydraulictransfer valve and a conduit means connecting said transfer valve withsaid end chambers and also with the cylinder of said second couple atopposite sides of the piston of said couple, there being a by-pass valveoperatively associated with said end chambers effective when opened toprevent hydraulic lock at said end chambers while said transfer valve isinoperative.

5. A hydraulically actuated servo mechanism comprising, in combination,a control valve, an input element: constituted by a valve spool in saidvalve, an output member movable in either of two directions, a housing,means including conduit means for pressurized fluid whereby said outputmember by action of said lluid can be moved in one of said directions orthe other according as said valve spool in response to an input from onesource is moved in one direction or the other, and an auxiliary meansresponsive to receipt thereby from a souce other than the first-namedone of an input in either of two directions for coaction with said valveto cause the output member to move in one or the other of said twodirections according as the input from said other source is in one orthe other of said two directions, the firstnamed means including acylinder and piston couple the cylinder of which is constituted by achambering in said housing, said valve having two chambers each outboardof one of the two ends of the valve spool, said couple including atubular piston rod carrying the piston, there being a second cylinderand piston couple of which the cylinder is inside said tubular pistonrod, there being secured to the housing a piston rod carrying the pistonof said second couple, said auxiliary means including further conduitmeans and an electro-hydraulic transfer valve operably associated withsaid further conduit means, said further conduit means connecting saidtransfer valve with one of said chambers and with the cylinder of saidsecond couple at one side of its piston and also connecting saidtransfer valve with the other of said chambers and with the cylinder otsaid second couple at the other side of its said piston.

6. A hydraulically actuated servo mechanism, comprising in combination:a housing including a cylindrical chamber for piston; a power outputpiston in said chamber; a control valve means including 4a valve spool,said control valve means adapted to supply hydraulic fluid un erpressure to reversibly move said housing relative to said piston; wallsdefining a valve spool control chamber `at each end ot said valve spool;an electro-hydraulic transfer valve operable to cause flow ot iluidunder pressure into either of said valve spool control chambers toposition said valve spool; a by-pass valve connecting said two valvespool chamber; an alternative means for moving said valve spoolindependently or" said electro-hydraulic transfer valve; means foropenin said by-pass valve when said alternative means is operating saidvalve spool; a double acting response piston moveable in a cylinder inresponse to relative motion between said power output piston and saidhousing; a conduit from each side of said response piston to one of saidvalve spool control chambers, whereby the operative eltect of liuid fromsaid transfer valve on said valve spool is reduced to an extentdetermined by the motion of said `response piston.

References Cited in the le of this patent UNITED STATES PATENTS 14Rockwell June 27, 1944 Cunningham July 18, 1944 Mott Oct. 14, 1952Cintron May 5, 1953 Parker Apr. 20, 1954 Chenery et a1. May 11, 1954Edwards Apr. 12, 1955 FOREIGN PATENTS Germany Mar. 23, 1953

